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igure 5: Sentinel-1 IW mode Sea Ice Thickness estimate, covering a large part of the Gulf of Bothnia on 10 February at 16:06:24 UTC. 
The Baltic Sea ice drift (SID) estimation algorithm (Karvonen 
2012) was replaced in December 2021 by a new algorithm 
utilizing feature matching with the ORB algorithm (Rublee 
et al., 2011) in low resolution and optical flow (Lucas and 
Kanade, 1981). The first phase included thorough tests 
to ensure stability and quality, and then refiningthe drift 
estimation using pattern matching by optical flow. The new 
ice drift algorithm has been validated by using the winter 
2017-2018 SAR data (Radarsat-2 ScanSAR wide mode HH/ 
HV and Sentinel-1 GRDM EW HH/HV) against drift from ice 
drifter buoys. 
The daily Baltic Sea SIT mosaic product merges the most 
recent Sentinel-1 EW HH/HV and Radarsat-2 ScanSAR 
wide HH/HV mode SAR Baltic Sea SIT products into daily 
mosaics covering the whole Baltic Sea, with the most 
recent SIT data available at each grid cell. The product has 
been avallable since January 2016. 
1.7 Global NRT sea ice drift 
ın 2015, the evolution of the NRT SID product was mostly 
driven by the new Sentinel 1A SAR platform, following a 
rather long period of sparse data from Radarsat2 after the 
demise of Envisat ASAR instrument in 2012. At the time, it 
consisted of NRT high accuracy high detail north or south 
pole sea ice covering measurement patches. The steadily 
increasing data volume gave a much improved coverage 
both spatially and temporally. This is crucial, given that 
the discrete tracking of sea ice requires spatial coverage 
af the same approximate area, with a temporal difference, 
in order to capture the displacement before the observed 
surface of the sea ice decorrelates significantly.